(1) Field of the Invention
The present invention relates to a process for preparing a zeolite molded body which is valuable as a catalyst in purification of petroleum or petrochemical industry or as an agent for the separation or purification of gases and liquids. More particularly, the present invention provides a process for preparing a synthetic faujasite molded body without using a binder.
(2) Description of the Related Art
A faujasite type zeolite is a naturally occurring aluminosilicate, and this zeolite is also artificially synthesized by Linde Division of Union Carbide Corporation. The synthesized zeolite is named "Zeolite X" or "Zeolite Y" and is generally called synthetic faujasite. Various processes for the synthesis of synthetic faujasite have been proposed. But, most of these processes are directed to the preparation of a synthetic faujasite crystal powder.
Where synthetic faujasite is used industrially as an adsorbent or catalyst, it is often difficult to use synthetic faujasite directly in the form of crystal powder, and therefore, a molded body having a spherical shape, a columnar shape or other appropriate shape is ordinarily used.
Since, however, particles of zeolite crystal powder have no mutual bondability, an organic or inorganic binder is ordinarily used to impart appropriate plasticity and mechanical strengths during the preparation of a molded body. As the inorganic binder, there are used, for example, clay minerals such as kaolin and montmorillonite, and silica sol and alumina sol. However, although a certain mechanical strength is maintained in the thus-prepared molded body, the zeolite component is diluted by the added binder and the amount of the binder must be increased to impart a mechanical strength sufficient for industrial applications. If this molded body is used as a catalyst, the clay mineral incorporated as the binder sometimes causes an undesirable side reaction.
As the substitute for the process for preparing a molded body by mixing synthetic faujasite powder with a binder, several processes have been proposed in which a molded body of a starting material mixture is first prepared and the molded body is crystallized to form a synthetic faujasite molded body having substantially the same shape as the shape before crystallization. For example, there can be mentioned processes proposed in Japanese Examined Patent Publications Nos. 40-746 and No. 53-33,557. In these processes, as in the case where synthetic faujasite powder is prepared, a nucleus-forming seed having a size of 0.01 to 0.05 micron, which is obtained by aging a starting material composition at room temperature for a long time or by aging the composition at a low temperature, must be added to the starting material mixture.
We found that the incorporation of a transparent faujasite germ solution is very effective for the formation of crystal nuclei in the preparation of synthetic faujasite powder. However, when this finding was applied to the preparation of a synthetic faujasite molded body, it was found that crystallization is not sufficiently advanced and impurities are readily formed, and a desired synthetic faujasite molded body cannot be obtained. This is thought to be because the effect of the used transparent faujasite germ solution was lost during the kneading or molding step.